3.从尾到头打印链表

/**
*    public class ListNode {
*        int val;
*        ListNode next = null;
*
*        ListNode(int val) {
*            this.val = val;
*        }
*    }
*
*/
import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> list=new ArrayList<>();
        if(listNode==null)return list;
        if(listNode.next==null){
            list.add(listNode.val);
            return list;
        }
        while (listNode.next!=null){
            list.add(listNode.val);
            listNode=listNode.next;
        }
        list.add(listNode.val);
        ArrayList<Integer> list1=new ArrayList<>();
        for(int i=list.size()-1;i>=0;i--){
            list1.add(list.get(i));
        }
        return list1;
    }
}

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class Solution {
    public class ListNode {
        int val;
        ListNode next = null;
        ListNode(int val) {
            this.val = val;
        }
    }
    public static ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        Stack<Integer> stack = new Stack<>();
        while (listNode != null) {
            stack.push(listNode.val);
            listNode = listNode.next;
        }

        ArrayList<Integer> list = new ArrayList<>();
        while (!stack.isEmpty()) {
            list.add(stack.pop());
        }
        return list;
    }
}